IDFT Handling during S1 Handover

The following illustration describes the IDFT handling during S1 handover with collapsed UPF.

IDFT Handling during S1 Handover Call Flow Description
Step Description
1

As part of initial attach, N4 and Sxa session is already established with SMF and UPF. S1 handoff is triggered.

The MME sends Indirect Tunnel Request Message to the SGW-C/cnSGW.

2

The SGW-C/cnSGW sends Sx Modify Request (Sxa) to the UPF. At UPF:

  • IDFT PDR is detected at SessMgr

  • New F-TEID is allocated for IDFT tunnel

  • Converged datapath is not required and traffic goes through Slowpath

3 The UPF sends Sx Modify Response (Sxa) to the SGW-C/cnSGW.
4 The SGW-C/cnSGW sends Create Indirect Tunnel Response Message to the MME.
5 The Source eNodeB sends IDFT data packet to the UPF. If there’s no matching 3 tuple stream at UPF, the packet is forwarded to SessMgr.
6 The UPF sends IDFT data packet to the destination eNodeB.